Recent years have seen the rapid development of various classes and types of CCD image sensors and their present widespread use in imaging systems for both amateur and professional applications. Their small size, electrical efficiency, cost-effectiveness, etc., have made CCD image sensors the imaging units of choice, not only for inexpensive consumer video cameras, but for more critical uses in professional or commercial applications such as, for example, in digital color printer applications and high-speed scanning applications.
Due to the nature of the manufacturing processes used to produce these relatively complex multi-level thin film structures, there is a constant effort directed to improve these multi-step fabrication efforts and device yields, by incorporating knowledge gained from testing completed and packaged CCD image sensors under various conditions such as, for example, conditions of elevated temperature, high illumination levels, and under conditions where higher levels of control signals are applied than required during normal operating conditions.
Currently employed test systems, while partially automated, rely largely on a number of individual control signal generators, each one of which is dedicated to providing the control signals required for the operation of a single CCD image sensor. This approach of using one dedicated control signal supply for each one CCD image sensor to be tested may be adequate in situations where testing is done on relatively few devices or relatively infrequently. The complexity, space requirements, and cost of using dedicated control signal supplies for testing CCD image sensors can be appreciated by considering a numerical example: if a manufacturer of CCD image sensors produces even as few as 20 packaged devices in a certain time period, these 20 devices would either have to be tested sequentially using one and the same dedicated control signal generator, or 20 control signal generators could be constructed or purchased at significant cost and space allocation considerations to then test each of the 20 sensors at about the same time side by side. If, for example, 20 packaged image sensors of each one of five types or classes are to be tested over a time period one faces the unenviable prospect of considering the design, construction or purchase of a total of 100 dedicated control signal generators, only 20 of which can be used to control respective ones of the sensors.
Thus, while it is clearly possible to use a dedicated control signal supply or a dedicated control signal generator to functionally test a single CCD image sensor (which may be a so-called mega-pixel imager having at least a million photodiode-like light sensitive pixels and an equally large number of shift register storage and charge transport regions of a semiconductor nature), it is nonetheless economically unattractive in view of the above examples. Another known test system dedicated to testing in a semi-automated manner a single device at a time is disclosed in U.S. Pat. No. 5,113,134, issued May 12, 1992 to Plus et al, in which a test circuit is used to test but a single liquid crystal display at a time, the display having numerous nominally identical thin film transistor elements within it as part of its design. Thus, the disclosure by Plus only applies to the sequential testing of individual liquid crystal display devices of one and the same type. The teaching provided in the disclosure of U.S. Pat. No. 5,113,134 does not appear to include selectability of the integrated test circuit so as to either make it adaptable to functionally test a plurality of same-type liquid crystal displays at the same time, or alternatively to adapt the integrated test circuit to be effectively usable to test different types of liquid crystal displays one display at a time.
Accordingly, it is highly desirable to provide a test system and method for dynamic testing at the same time of a plurality of packaged CCD image sensors.
It is desirable to provide a versatile test system which can be readily changed and adapted to test a plurality of a different class or type of CCD image sensors.
And it is desirable to provide a test system having the number of interconnections between a control signal generating portion of the system and another portion of the system (which accommodates the plurality of CCD image sensors to be tested) be no larger than the number of connections required by an individual CCD image sensor.